1. Field
The present invention relates to a method of quenching a ring shaped article such as, for example, a bearing raceway ring or the like, which is performed while correction of a thermal deformation of the ring shaped article is carried out, and an apparatus accomplishing such quenching.
2. Description of the Related Art
If such a ring shaped article as a raceway ring or the like of a bearing assembly is quenched, a deviation may occur in the circularity as a result of thermal deformation. For this reason, after the quenching, a process of correcting such deformation is generally practiced with the use of a ring shaped deformation correcting jig.
However, if correction of the deformation is carried out at a process step separate from the step of quenching, the number of process steps in the manufacturing line for the production of ring shaped articles will increase and, therefore, as shown in FIG. 10, the deformation is corrected when quenching by cooling the ring shaped article W inserted into an arresting die 40. More specifically, after the ring shaped article W has been heated to a quenching temperature (about 850° C.), the ring shaped article W is cooled down to a temperature near to a martensitic transformation point (martensitic transformation temperature: 230° C.) without being restrained in any arresting die; when it is cooled down to such temperature, the ring shaped article W is placed inside the arresting die 40 and is then cooled down to a predetermined temperature (about 110° C.); after the ring shaped article W has been cooled down to such temperature, the ring shaped article W is removed from the arresting die 40; and thereafter the ring shaped article W is allowed to cool naturally down to room temperature.
Also, as one method of correcting the deformation with the use of the arresting die, the method has been suggested, in which using the arresting die of an axially elongated and vertically extending cylindrical configuration, a ring shaped article then at a cooling step of the quenching process is forcibly inserted into the vertically cylindrical arresting die sequentially from above so that the ring shaped article within the arresting die can be pushed sequentially outwardly from below. For example, see Japanese Patent Publication No. H09-176740.
It has, however, been found that the deformation correcting method utilizing the arresting die as hereinabove described requires the arresting die, which tends to incur a high manufacturing cost, to be prepared for each of ring shaped articles of different dimensions. Also, a work of mounting the ring shaped article in the arresting die and a work of removing the ring shaped article from the arresting die after completion of the quenching require a substantial amount of labor. In the case of the deformation correcting method disclosed in Japanese Patent Publication No. H09-176740 referred to above, no work of removing the ring shaped article from the arresting die is needed, but since in this method, the ring shaped article is retained within the arresting die by the effect of a frictional force developed between the arresting die and the ring shaped article, there is the possibility that the ring shaped article of a large dimension tends to fall downwards from the arresting die by the effect of its own weight and, therefore, such method is merely applicable to ring shaped articles of a relatively small dimension.
In view of the above, it has been desired to develop the technology by which without incurring any cost and a labor, thermal deformation of ring shaped articles of varying sizes can be corrected.
Also, a continuous heating furnace largely employed in the conventional quenching apparatus has such problems that it requires the use of a substantial length of the path of travel of an article to be heated in order for the latter to be heated to a quenching temperature and that the equipment tends to become bulky in size. Accordingly, it has been desired that the quenching method and the quenching apparatus, both based on the foregoing technology, require the heating time, which is short, and heating facilities which are compact.